Basis of Presentation and Significant Accounting Policies - Schedule of Changes in DAC due to Adoption of ASU 2018-12 (Details) - USD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs	$ 331.6	$ 330.6
Whole Life
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs	21.2	20.9	$ 19.1	$ 17.8
Term Life
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs	30.7	30.0	27.5	25.6
Experience Life
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs	5.8	5.8	6.0	6.2
Limited Pay Whole Life
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs	6.8	6.7	5.6	4.4
Indexed Universal Life
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs	15.7	15.4	13.7	12.9
Supplemental Health
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs				4.3
Total Annuities
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs	$ 219.7	221.1	$ 223.3	223.1
Previously Reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs		433.1
Previously Reported | Whole Life
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs				17.8
Previously Reported | Term Life
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs				25.6
Previously Reported | Experience Life
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs				2.6
Previously Reported | Limited Pay Whole Life
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs				4.4
Previously Reported | Indexed Universal Life
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs				11.3
Previously Reported | Supplemental Health
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs				4.3
Previously Reported | Total Annuities
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs				137.7
Effect of the Adoption of ASU 2018-12
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs		$ (102.5)
Effect of the Adoption of ASU 2018-12 | Whole Life
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs				0.0
Effect of the Adoption of ASU 2018-12 | Term Life
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs				0.0
Effect of the Adoption of ASU 2018-12 | Experience Life
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs				3.6
Effect of the Adoption of ASU 2018-12 | Limited Pay Whole Life
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs				0.0
Effect of the Adoption of ASU 2018-12 | Indexed Universal Life
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs				1.6
Effect of the Adoption of ASU 2018-12 | Supplemental Health
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs				0.0
Effect of the Adoption of ASU 2018-12 | Total Annuities
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs				$ 85.4